Coolant leak passenger near rear tire
 

We have a 2000 Boxster that has never given a moment of trouble.. Recently it started pushing out about 2 litres of coolant after a longer drive. Our local shop checked it out and the only thing they found was a minor leak in the coolant filling tank. We changed that and still have the exact same issue. My gut says thermostat, but even when driving it doesn't overheat, and only pushes the coolant out after shutting off the motor. Cooling fans are coming on, both from radiators where changed about 3-4 years ago.

Appreciate any ideas or suggestions.

Water pump?
I changed mine, when I installed a new coolant tank in the rear trunk.

You didn’t say where the cooling was leaking. Is it immediately under the front of the engine or is it further back towards the expansion take. You could have a leak in the hose to the overflow expansion tank? If it were the thermostat or water pump the leak would be immediately under the front of the engine not further back towards the expansion tank. You also didn’t say how fast or how much it was leaking but I assume it’s slow which makes me think it’s a hose leak. Water pump leaks have visible stains on the engine block and assembly. The cooling hose plumbing on the boxster is complex, see these diagrams

https://einmaligparts.3dcartstores.com/Water-Cooling-System_c_7818.html